smell in basement from non-vented kitchen sink

We purchased an older home about six months ago and discovered that the previous owners had done all the plumbing work in the kitchen themselves and hadn't done a very good job. The kitchen pipes were connected to the washing machine pipes and neither were vented. We soon discovered that when we would do a large amount of dishes in the kitchen sink, we'd get a sewer gas smell in the basement - but not in the kitchen. We had several plumbers come to see if we could fix the problem without installing a vent through the roof. Both plumbers were confused by the fact that we never smelled the sewer gas smell in the kitchen - just in the basement. They thought that when we did dishes in the kitchen and water rushed down the pipes, it sucked the water out of the p-trap in the laundry piping - so they redid the kitchen piping to separate it completely from the laundry and thought that would fix the smell issue. Then last night, we did the dishes and again the smell was back.

Obviously the fundamental problem is the lack of venting, but why does the smell only occur in the basement and not in the kitchen? This has puzzled the two different plumbers we've had out to our house. Is there any way to fix this besides the considerable work that would go into properly venting the kitchen sink through the roof? We already spent a considerable amount of money trying to fix this already with no success. Thanks for your help!

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smell in basement from non-vented kitchen sink

I'd get a new plumber out there. The easiest way to diagnose smells is with a smoke test, and if neither of them suggested it you need a better service guy . BTW a smoke test will find any leaks in the dwv system, you pump thick smoke into the pipes and seal all vents. Smoke will come out of blown trap seals, breaks, ect.

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smell in basement from non-vented kitchen sink

Thanks. I do wish that the past two plumbers had suggested a smoke test - or that I had thought to ask. But what they had said was that if there was a leak, then we would smell the sewer gas more often, as opposed to just when we do dishes. That confuses me as well. Is it possible that there could be a leak in the basement pipes that come from the kitchen that would cause the sewer gas smell to be released into the basement, but only after we do dishes and send a large quantity of water down the pipes (keeping in mind again that the kitchen sink is not vented...)

smell in basement from non-vented kitchen sink

See if you can install an under-sink-base air admittance valve.
They allow air into the drain line, but will not allow the sewer gas out, and are made just for this type of situation.
Good luck (and get a new plumber).
Mike